The disclosure of Japanese Patent Application No. 2000-164923 filed on Jun. 1, 2001 including the specification and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a catalyst deterioration detecting device and a catalyst deterioration detecting method for detecting the deterioration of exhaust emission purifying catalyst arranged on an exhaust passage of an internal combustion engine.
2. Description of Related Art
Exhaust emission purifying catalyst (hereinafter, also simply referred to as catalyst) for purifying unburned fuel, carbon monoxide, nitrogen oxide or the like in the exhaust gas is attached to an exhaust passage of an internal combustion engine mounted in a vehicle. Also, a catalyst deterioration detecting device to determine a deteriorating state of the catalyst is also concomitantly installed to the internal combustion engine in order to prevent an increase in an emission amount of unpurified components into the atmosphere due to the deterioration of the catalyst. As such a catalyst deterioration detecting device, one described in Japanese Patent Laid-Open Publication No. Hei 5-163989 etc. is known. The catalyst deterioration detecting device described in this publication has air-fuel ratio sensors upstream and downstream of an exhaust emission purifying catalyst, respectively, and detects the deterioration of the catalyst based on the outputs of these air-fuel ratio sensors.
In the invention according to the above-mentioned publication, however, the determination of the deterioration of the catalyst was carried out by simply comparing an index characteristic value of catalyst deterioration (specifically, a locus length ratio or an area ratio) derived from the outputs of the pair of air-fuel ratio sensors at a certain time point and a reference value for comparison. However, with various deterioration forms of catalyst, there are possibilities that all these various forms cannot be positively detected by the above-mentioned method. Therefore, development of a catalyst deterioration detecting device capable of performing more advanced determination of the deterioration of the catalyst has been wanted.
It is an object of the invention to provide a catalyst deterioration detecting device and a catalyst deterioration detecting method capable of detecting the deterioration of exhaust emission purifying catalyst more positively and in an earlier period of time, regardless of form of deterioration.
In order to achieve the object, the first form of the invention comprises exhaust emission purifying catalyst on an exhaust passage of an internal combustion engine, and at the same time air-fuel ratio sensors provided at upstream and downstream of the exhaust emission purifying catalyst, respectively, wherein deterioration of the exhaust emission purifying catalyst is detected based on the outputs of the air-fuel ratio sensors. At that time, an index characteristic value of catalyst deterioration is calculated from the outputs of the air-fuel ratio detecting means, a time-lapse changing ratio of the index characteristic value of catalyst deterioration is calculated, and the deterioration of the exhaust emission purifying catalyst is thereby determined based on the time-lapse changing ratio.
According to the invention, the deterioration of the exhaust emission purifying catalyst is determined based on the time-lapse changing ratio of the index characteristic value of catalyst deterioration; therefore, it is possible to detect the deterioration of the exhaust emission purifying catalyst more precisely corresponding to various deterioration forms of the exhaust emission purifying catalyst. Since the deterioration of the exhaust emission purifying catalyst is determined at this time based on the time-lapse changing ratio of the index characteristic value of catalyst deterioration, it is possible to detect the deterioration in an earlier period of time and further suppress the emission of hazardous substances into the atmosphere.
When the time-lapse changing ratio is calculated, the calculation is desirably based on population shifted along the time-series. With this calculation, even in a case where an abnormality index characteristic value of catalyst deterioration is indicated sporadically without having a deterioration state of the exhaust emission purifying catalyst, it is possible to prevent the exhaust emission purifying catalyst from being incorrectly determined as deteriorating and further precisely carry out the detection.